Ok, are you connecting to it via a patch cable or via a wireless connection?
If you are connecting wirelessly, there are a couple of possibilities. First, try turning off Wireless Encryption Protection WEP and see if your connection improves. Also, next time your connection is lost, look outside and see if anyone is using a garage door opener. Other possible culprits can include wireless phones, cell phones, microwaves in line between the base station and the wireless card, etc. How far away is your computer from the router?